Contact lenses have been in existence for many decades. Early contact lenses were made of glass or rigid plastic such as polymethylmethacrylate (PMMA). Early contact lens designs were quite large and referred to as scleral or haptic lens. Scleral or haptic contact lens designs cover the cornea completely as well as covering a large portion of the conjunctiva or sclera of the eye. The sclera is the structural white of the eyeball while the conjunctiva is a transparent tissue which overlies the sclera as well as covering the backside of the eye lids. Early contact lens designs were made of rigid, largely oxygen impermeable polymers as discussed above or a very few of glass. Because cornea physiology was poorly understood at the time these lenses were made, they often cause great discomfort and negative effect on the corneal health.
As time went by, in the 1950's, hard contact lenses made of polymethylmethacrylate became much smaller having a diameter significantly smaller than that of the cornea. Hard corneal contact lenses were more comfortable and less physiological damaging than scleral or haptic lenses, but only marginally so. Hard contact lenses still significantly deprived the cornea of a necessary oxygen supply from atmospheric oxygen to maintain good corneal health and were difficult to adapt to. In the 1970's, so called soft corneal contact lenses became available. Soft contact lenses generally are larger than hard corneal contact lenses having a diameter approximating that of the cornea, somewhat larger than the cornea or somewhat smaller than the cornea. Soft contact lenses are generally made of hydrophilic polymers, such as polyhydroxy ethylmethacrylate (poly HEMA), that absorb substantial amounts of water, saline solution or the tear film. Soft contact lenses also provided improved comfort due to their permeability to oxygen and due to their more flexible nature. Later still, so called gas-permeable contact lenses became available. Gas permeable rigid contact lenses are similar in size and structure to hard corneal contact lenses but are made of rigid oxygen permeable polymers that allow oxygen and other gases to pass through the material of the contact lens to provide improved corneal health. Generally, rigid contact lenses provide sharper vision than soft contact lenses though this is not universally true.
Hard contact lenses are well as scleral or haptic contact lenses were sometimes fenestrated. That is, tiny holes were drilled or otherwise formed through the rigid contact lens material in an effort to improve tear exchange under the contact lens or to provide a greater availability of oxygen through the contact lens. Fenestration was generally not a very successful technique. Fenestrations, however, were uniformly tiny holes generally much smaller than one millimeter in diameter, occasionally multiple fenestrations were present.
All contact lenses known to the applicant provide substantially or complete coverage of the cornea of the eye.
Drug delivery inserts are also known to exist. Drug delivery inserts are small containers into which drugs or pharmaceuticals are placed or absorbed that exist in several different forms. Subpalpebral drug delivery inserts are generally intended to be inserted behind the eye lid in the conjunctival fornices and to gradually release a desired medication to provide a slow, continuous supply of drug to the eye. Subpalpebral drug delivery inserts generally have suffered from being uncomfortable for the patient to tolerate and subject to be accidentally dislodged from the eye by rubbing of the eye or other movements. In addition, subpapebral drug delivery inserts sometimes cause irritation of the conjunctiva or the eye lids.
Another variety of drug delivery insert is intended to be surgically inserted within the globe of the eye to gradually leach out a steady supply of a desired drug into the intraocular environment. Intraocular drug delivery inserts are less often used due to their relatively invasive nature.
Generally, drug delivery inserts whether subpalpebral or intraocular have contained a single drug.
Dry eye syndrome is one of the most commonly treated eye problems in the United States. Dry eye syndrome is also known as keratitis sicca, keratoconjunctivitis sicca (KCS) xerophthalmia, and lacrimal insufficiency. It is estimated that over ten million Americans and 30 million persons worldwide suffer from dry eye syndrome.
For a large fraction of dry eye patients, dry eye syndrome creates discomfort or annoyance. For those severely afflicted, dry eye syndrome can be debilitating and, in some circumstances, even sight-threatening. In extremely severe cases, dry eye syndrome can even lead to the loss of an eye.
Dry eye syndrome typically results from deficiency in the quality or quantity of tears produced by the patient. Precorneal tear film has traditionally been considered to have a three-layered structure. Closest to the cornea lies the mucin, or mucus, layer. The mucin layer provides an interface between the corneal epithelium and the remainder of the tear film. Overlying the mucin layer is the watery aqueous layer, which is the thickest layer of the three. The outermost layer of the precorneal tear film is the lipid layer. The lipid layer is an oily film that reduces evaporation from the aqueous layer beneath it.
The middle aqueous layer provides moisture to the corneal tissue, carries important nutrients, and serves to remove metabolic waste produced by the cornea. Deficiency in any of the three layers of the precorneal tear film can result in complaints of dry, gritty feeling or burning eyes.
The mucin that forms the mucin layer, nearest the cornea, is secreted by goblet cells in the conjunctiva. The conjunctiva is the transparent tissue that covers the sclera and the backside of the eyelids. The mucin layer functions to decrease surface tension of the tear film. In addition, the cornea itself is hydrophobic. Without the mucin layer to provide a bridge between the cornea and the aqueous layer, the aqueous layer would bead up and allow dry spot formation on the cornea.
The aqueous layer is secreted primarily by the glands of Wolfring and Krause located in the eyelid margin. The aqueous layer helps provide an optically smooth, transparent surface to the precorneal tear film. The lipid layer is secreted by the meibomian glands, and the glands of Zeiss and Moll. The glands of Zeiss and Moll are also located at the eyelid margin.
Blinking is essential to maintenance of the precorneal tear film. During each blink, the eyelid wipes over the surface of the cornea, smoothing the mucin layer and spreading the overlying aqueous and lipid layers to provide a completely wetted surface. In between blinks, the tear film thins due to evaporation of the aqueous layer. If evaporation is excessive, dry spots may form on the surface of the cornea.
Deficiency, or imperfect quality, of any of the three component layers can lead to dry eye symptoms. Many systemic and external factors can contribute to dry eye syndrome. For example, Sjogren's syndrome is associated with arthritic diseases in combination with dry eye and dry mouth. Deficiency of Vitamin A, use of oral contraceptives and environmental factors can all contribute to dry eye syndrome. Inflammation has also been demonstrated to contribute to dry eye.
Research into the natural history of dry eye syndrome suggests that the disease progresses through four stages. Each stage is a consequence of the preceding stage. The stages are:                1. Loss of water from the aqueous layer of the tear film leading to an increase in the tear film osmolarity;        2. Loss of conjunctival goblet cells and decreased corneal glycogen;        3. Increased loss of corneal squamous epithelial cells;        4. Destabilization of the interface between the corneal surface and the tear film.        
Either decreased secretion of tear film components or increased evaporation lead to increased tear film osmolarity and the following stages that lead to eventual corneal decompensation and the serious consequences of dry eye syndrome.
The adnexa of the eye may also be involved in dry eye syndrome. The adnexa of the eye include the structures surrounding the eye such as the eyelids, eye lashes, the tear drainage and tear production structures. Blepharitis commonly contributes to dry eye syndrome. Blepharitis typically results from bacterial infection of the tiny glands in the margin of the eyelid. These glands include the glands of Zeiss, Moll and Wolfring as well as the meibomian glands. Most commonly, the affected glands are the meibomian glands. In bacterial blepharitis, bacterial infection causes the meibomian glands to become plugged, and thus not be able to produce a normal lipid layer to contribute to the tear film. Some bacteria that infect the glands also secrete exotoxins that seep out of the glands into the eye and injure the corneal epithelium.
Treatments of dry eye syndrome vary depending upon the type of presentation. The most common treatment for dry eye syndrome is the use of artificial tear supplements to provide additional moisture and lubrication to the corneal surface. Artificial tear eye drops are placed on the eye by the patient. Artificial tear supplements must be used regularly and often to be effective.
Lubricant ointments may also be employed. Ointments are usually used at bedtime because they tend to be messy and blur vision. For some patients, even the use of ointments is not sufficient to provide comfort during sleep.
Tears drain from the eye through the lacrimal drainage system. Tiny openings at the nasal corner of each upper and lower eyelid are called the lacrimal puncta. The lacrimal puncta lead into ducts that drain into the nasopharynx.
One treatment for dry eye syndrome is to partially or completely close one or more lacrimal puncta to reduce tear outflow into the lacrimal drainage apparatus. Traditionally, this closure was accomplished surgically or by cautery. In the last decade, however, temporary and permanent punctal occlusion plugs have been utilized.
Permanent punctal plugs are typically made from surgical silicone; temporary plugs are generally made of soluble collagen. Collagen plugs dissolve over a period of days and are helpful in diagnosis.
Punctal plugs are placed into the lacrimal puncta, or lacrimal drainage ducts. The plugs impede the outflow of tears from the eye. This approach slows the outflow of tears and retains them in the eyes longer, often relieving symptoms. Punctal plugs have the distinct advantage of being readily removable and avoid the issues of scar formation.
Blepharitis is sometimes treated by the use of antibiotic medications. Another important treatment for blepharitis is the application of warm soaks and lid scrubs. In this form of treatment, the patient applies a warm wet washcloth to the eyelids for a period of time to provide humidity, warmth and to help soften blockage of and restore flow from the meibomian glands. Lid scrubs are practiced by taking a mild, nonirritating soap and vigorously scrubbing the eyelid margins with they eyes closed, so as to massage the meibomian glands and increase production. The surfactant helps to dissolve the greasy blockage of the meibomian glands.
Patients who have severe dry eye syndrome often suffer disrupted sleep because they cannot go for longer than an hour or so without applying tear supplements to the eyes. This can lead to pronounced sleep deprivation and a consequent reduction in quality of life.
A variety of researchers have been seeking other medicinal treatments for dry eye syndrome. Largely, this research is directed at pharmaceutical efforts to increase tear production.
Accordingly, there is still room for improvement in the contact lens related.